I swore I wasn't going to become a regular poster...
...My suspicion is that the update servers will ignore a request if they are too busy, or perhaps if they receive multiple requests simultaneously, or something along those lines. I do know for a fact that sitting there clicking "Retry" repeatedly had no effect, but when I did "the trick" all the way through, repeatedly, after the sixth try or so it went through and was suddenly downloading (no warning or "click OK"; it just started downloading). So I believe "the trick" does have an effect of some sort, perhaps it alters the form ("wording"?) of the request the phone itself sends. To those who haven't gotten it yet: rest easy, maybe try it a few more times tonight, or just get some sleep and try it tomorrow. But don't give up after the first three tries. It's a hassle to go through the entirety of "the trick", but do it at least ten or twelve times in a set. It'll come eventually.
And like people have said - it's not life-changing, but you will definitely notice the difference on your home screens. The transition animations have gone from slide show to, well, butter. The first few scroll attempts might look a little clunky, I guess while the animation is coding itself for the first time or something, but it smooths out fast. Also: make sure you reboot, I think, three times: the phone reboots itself once, where you'll see "optimizing apps" and the new Nexus "x" boot animation (way less gaudy, bravo); but reboot it again even if not prompted, as mine did some further updating when I did reboot it.
Happy Jelly Bean weekend!
